Some fuel cells include a polymer-electrolyte membrane (PEM). The PEM may be disposed between a catalyzed anode of the fuel cell, where electrochemical oxidation of a fuel takes place, and a catalyzed cathode of the fuel cell, where electrochemical reduction of oxygen takes place. These reactions may require the transport of one or more charged species (e.g., ions) across the PEM, from anode to cathode. Therefore, the PEM should be adequately conductive to the one or more charged species. If the PEM were not adequately conductive to the one or more charged species, undesirable internal resistances would result, thereby reducing the efficiency of the fuel cell.
In addition to being adequately conductive to the one or more charged species, the PEM should be substantially impervious to the fuel and to oxygen. If the PEM were not substantially impervious to the fuel and to oxygen, either or both of these species could traverse the PEM and react directly with the other, reducing the efficiency of the fuel cell and forming a potentially unsafe mixture of fuel and oxygen.
Some HT-PEMs can be gel-like, comprising a polymer matrix in which a liquid electrolyte is sorbed. One such PEM is denoted PBI-PA. In the PBI-PA membrane, phosphoric acid (PA) is sorbed into a polybenzimidazole (PBI) membrane. The PBI-PA membrane finds use in various fuel cells in which protons (H+) are conducted across the PEM from the anode to the cathode. Maintaining the operating performance of such fuel cells requires preserving both the proton conductivity of the PEM and its imperviousness to fuel and oxygen.